The background art of the invention is described with reference to the electric motor illustrated in FIG. 5. The electric motor includes an electric motor shaft 1, a rotor 2 which rotates about the electric motor shaft 1, a stator 3 disposed in an outer periphery of the rotor 2, a housing 4 having a tubular shape to house the rotor 2 and the stator 3, and an end cover 5 to be mounted on an axial end of the housing 4. The electric motor is placed in a vertical attitude of disposing the electric motor shaft 1 vertically, as exemplified by a slewing electric motor for an excavator. In the following, the axis direction of the electric motor may be called as up and down directions in the conventional art illustrated in FIG. 5 and in each of the embodiments of the invention to be described later, based on the aforementioned configuration. The upper side and the lower side in the drawings may be called as an upper portion (or an upper side) and a lower portion (or a lower side) of the electric motor. Besides, the “electric motor” described in the specification involves either of a generator and a generator motor configured to generate electric power by the same principle as the electric motor.
The end cover 5 is mounted on an upper end surface of the housing 4 with no-graphically-shown bolts. The upper portion of the electric motor shaft 1 is rotatably supported on the end cover 5 and the lower portion of the electric motor shaft 1 is rotatably supported on the lower portion of the housing 4, via respective bearings 6 and 7.
The stator 3 includes a stator core 8 constituted of laminated electromagnetic steel plates, and a stator coil 9 wound around the stator core 8 in up and down directions i.e., in the axis direction of the electric motor shaft 1 (hereinafter, also called as an electric motor axis direction). The stator coil 9 includes coil ends 9a which are respective turning portions on upper and lower sides, being wound so as to protrude the coil ends 9a beyond respective axial opposite ends of the stator core 8 in the electric motor axis direction.
The electric motor further includes a sealing body 10. The sealing body 10 is formed by potting sealant through an upper die into the housing 4 as a receiving die or a lower die in the state that the stator coil 9 has been wound and the stator 3 has been inserted into the housing 4. Used as the sealant is, for example, synthetic resin material such as unsaturated polyester having electrical insulation property and heat conductive property. The thus formed sealing body 10 covers at least the coil ends 9a, specifically, covers the entirety of the stator 3 or a part of the stator 3 including the coil ends 9a, thereby enhancing the heat conductive property from the stator 3 to the housing 4.
In the resin molded electric motor as described above, there may be disposed a temperature sensitive device S in the housing 4. The temperature sensitive device S is a device to be operated in response to temperature, for instance, a temperature measuring device for detecting a temperature of an electric motor such as a thermistor, or a temperature protection device for preventing excessive heating such as a temperature fuse. The temperature sensitive device S is generally embedded, as shown in FIG. 5, in the sealing body 10 together with the coil ends 9a. Hereinafter, the electric motor having the above configuration is called as an embedded type of electric motor (see Patent Literature 1 and Patent Literature 2).
There is also known an electric motor including a recess portion formed in a surface of a sealing body 10 and a temperature sensitive device is fixed by a bracket while being accommodated in the recess portion. Hereinafter, the electric motor having the above configuration is called as a retrofitted electric motor (see Patent Literature 3 and Patent Literature 4).
The conventional embedded electric motor and retrofitted electric motor, however, have the following disadvantages.
The embedded type of electric motor, where the temperature sensitive device S is embedded in the sealing body 10, can be easily assembled, but is unable to be repaired or replaced when inspected or being in trouble; the electric motor, therefore, has to be entirely replaced in the event of failure. Besides, there is a possibility that the resin injection pressure for molding the sealing body 10 acts on a soldered portion in the temperature sensitive device to bring the portion into damage or failure.
On the other hand, the retrofitted type of electric motor, which can be easily inspected, repaired, and replaced, has an excellent maintenance performance, but cannot be easily assembled because of involving a bracket for fixing the temperature sensitive device to prevent it from removal from the recess portion.